1. Field of the Invention
This invention relates to wireless transmitters and receivers and, more particularly, to frequency dividers.
2. Related Art
Harmonics contained in signal processing devices are a major cause of signal distortions. One case where harmonics can be especially problematic is in a limiter that is driven by a poly-phase filter. For example, standard 90° poly-phase outputs take the form of:0° output=input/(1+jwRC)90° output=input*(jwRC)/(1+jwRC)Based on this property, harmonic components in the output will be amplitude mismatched and will be phase shifted from the fundamental frequency. Therefore, the presence of harmonics at the input of a poly-phase filter can cause a shift in the zero-crossings at the output of the poly-phase filter. This shift can, in turn, cause an effective phase error when the output of the poly-phase filter is passed through a limiter that reacts primarily to zero crossings.
A second case where harmonics can cause signal distortions is in mixers. The presence of harmonics in a mixer input signal can result in odd-order mixing products (“OMPs”) in the mixer's output. An OMP, which is defined as the product of one input and an odd harmonic of another input, can cause signal distortions when its frequency is too close to the frequency of a desired mixer output signal. Other cases where harmonics can cause signal distortions include, for example, where unwanted harmonics couple across a circuit.
Therefore, there exists a need for signal processing systems that have reduced harmonic content.